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International Society for Infectious Diseases <http://www.isid.org>

Date: January 2008
Source: The British Society for Plant Pathology, New Disease Reports 2008; 16 [edited]
<http://www.bspp.org.uk/ndr/jan2008/2007-101.asp>

[ref: HY Wang et al: 1st report of _Beet mosaic virus_ infecting lettuce, in China. BSPP New Disease Reports 2008; 16]

_Beet mosaic virus_ (BtMV) is a species of the biggest plant virus genus, _Potyvirus_. It is widespread and mainly infects plants belonging to the families _Chenopodiaceae_, _Solanaceae_, and _Fabaceae_. In 1981, BtMV was
found in spinach (_Spinacia oleracea_) in Beijing, China. So far, only a few isolates from USA, Slovakia, Germany, China, and UK have been molecularly characterized, mostly from beet (_Beta vulgaris_).

From 2004 to 2006, a series of field surveys were conducted in Tai'an, Shandong Province, China, to investigate the viruses infecting vegetables. Lettuce plants (_Lactuca sativa_) showing symptoms of mosaic, puckering,
and severe stunting were found in several fields, with an incidence of 30-40 per cent. These samples showed positive reactions with antisera to _Potato virus Y_ (PVY) and _Turnip mosaic virus_ (TuMV) [both genus _Potyvirus_], and negative reactions with antisera to _Cucumber mosaic virus_ (CMV) [genus _Cucumovirus_], _Tobacco mosaic virus_ (TMV) [genus _Tobamovirus_], and _Potato virus X_ (PVX) [genus _Potexvirus_] indicating that a potyvirus was present.

The virus was analysed by RT-PCR [reverse transcription polymerase chain reaction] specific to potyviruses. The resultant 1629 bp [basepair] fragment sequence (isolate named BtMV-SD) indicated that the virus is BtMV, which was further confirmed in western blotting with antiserum provided by Prof. C Han of China Agricultural University. Sequence alignment showed that the 3'-terminal genomic sequence of BtMV-SD shared 91.1-98.8 per cent identity at nucleotide level with other BtMV isolates available in the GenBank database, while the CP [coat protein]-encoding sequence shared 92.4-99 per cent identity at nucleotide level, and 97.5-100 per cent
identity at amino acid level with other BtMV isolates. BtMV isolates can be divided into 2 groups, a Euroasia group and an America group. BtMV-SD clusters with the Euroasia group and forms a common branch with isolate REN-1 from Slovakia.

Lettuce is reported to be susceptible to more than 50 viruses. However, to our knowledge, this is the 1st report that BtMV can naturally infect lettuce.

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[BtMV is distributed worldwide in major beet-growing areas. Besides _Beta_ species, hosts include spinach, clover, some cucurbit and leguminous vegetables, and a number of weed species. Early infection can reduce root yield of sugar beet by almost 10 per cent. On most host species, BtMV causes distortions, discolouration, and mosaic symptoms on leaves affecting the photosynthetic potential of the plant. In mixed infections in sugar beet with some other beet yellowing viruses of different genera (for example _Beet yellows virus_, _Beet western yellows virus_) it causes synergism resulting in faster disease progression, severe stunting, and increased yield losses. These synergistic effects often lead to higher virus levels and are more pronounced in susceptible beet varieties, but are also observed in varieties exhibiting tolerance to the viruses.

BtMV is spread by more than 28 species in the aphid family, but the principal natural vectors are reported to be _Myzus persicae_ (peach aphid) and _Aphis fabae_. The virus can also be transmitted by mechanical means and grafting, but is not transmitted in seed or pollen. Disease management includes phytosanitary measures, control of vectors and pathogen reservoirs, and use of resistant crop varieties if available.

With this report of lettuce being affected by BtMV, another economically important host of the virus has been found. BtMV exhibits synergistic effects in sugar beet with _Beet western yellows virus_, and this virus has previously been reported in both sugar beet and lettuce in China (see ProMED-mail post no. 20070516.1564). The possibility that synergistic effects may occur also in lettuce with this and other viruses of the crop must considered.

Maps
China:
<http://www.chinapage.com/map/map.html> and
<http://healthmap.org/promed?v=36.5,103.9,4>
Provinces of China:
<http://www.sacu.org/provmap.html>
Shandong Province:
<http://www.maps-of-china.com/shandong-s-ow.shtml>
Pictures
BtMV symptoms on sugar beet:
<http://www.ars.usda.gov/sp2UserFiles/person/2273/viruses2a.jpg> and
<http://www.rothamsted.ac.uk/broom/clinic/clinicimages/yellow_leaves/small-beet-mosaic.jpg> 

_Potyvirus_ particles, electron micrograph:
<http://www.ncbi.nlm.nih.gov/ICTVdb/WIntkey/Images/a1.gif>
_M. persicae_:
<http://plante-doktor.dk/myzus%20persicae1.jpg>
Links
Information on beet viruses including BtMV:
<http://www.rothamsted.ac.uk/broom/clinic/nyellow.php>
Genetic map of BtMV:
<http://genes.pp.ksu.edu/SP2UserFiles/person/24676/Beet_Mosaic_Virus.pdf>
Synergism of BtMV with other beet yellowing viruses:
<http://www.ars.usda.gov/research/publications/publications.htm?seq_no_115=160142> 

BtMV taxonomy and description:
<http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/00.057.0.01.010.htm>
Genus _Potyvirus_ taxonomy and species list:
<http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/57010056.htm>
Taxonomy of all other viruses via:
<http://www.ncbi.nlm.nih.gov/ICTVdb/Ictv/index.htm>
Information on aphids (with pictures):
<http://plante-doktor.dk/bladluseng.htm>. - Mod.DHA]